1. Field of the Invention
This invention relates generally to a system for manufacturing fluorescent lamp tubes having a circular form, and more particularly to a high speed system using a plurality of carrier devices, each of which returns to its starting position after passing around the various working stations in the manufacturing operation.
2. Description of the Prior Art
In manufacturing fluorescent lamp tubes having a circular form, it is necessary to bend glass lamp tubes having a straight or elongate form into such circular shaped tubes after first performing a tube softening operation thereon. The bending must then be carried out before the lamp tubes are cooled because of the increase of the rigidity thereof that occurs after such cooling takes place. For this reason, the bending working station is located close to the tube softening working station, usually being located on the same turn-table, which is divided into the respective functional parts of the different working stations.
It is also known that after bending the tube into its circular form, about 10 seconds cooling time is required in order to prevent the deformation or breaking thereof.
In the prior art, the bending operation is carried out by a roller, as shown in U.S. Pat. No. 3,215,518, which winds up the straight tube around its periphery to form the circular tube. The circular tube so produced, however, cannot be released immediately from the roller because of the reason described above, that is, because of the cooling time required. Thus, as the roller is occupied by the bended, and now circular, lamp tube, the next consecutive straight lamp tube being fed from the tube softening working station therefore cannot be immediately wound upon the roller for shaping. This means that, after each bending operation, the lamp tube-manufacturing process is interrupted, or must be momentarily stopped, regardless of the actuation of the other operations.
In view of this disadvantage, it is easy to imagine a bending apparatus which provides a large number of rollers for forming a similar large number of circular lamp tubes at the same time. However, such an apparatus tends to give rise to other disadvantages, such as, for example, complexity of the mechanism or very large turn-tables, and an increase of the peripheral velocity, which affects the formation of the lamp tubes, especially when the turn-table begins to rotate or stop.